It is well known to use protection devices capable of protecting electrical or electronic apparatuses from overvoltages that may result, for example, from lightning.
These protection devices usually comprise one or more overvoltage protection components, such as, for example, a varistor or a spark gap. In general, such protection components have two terminals enabling the protection components to connect to the installation to be protected. When the protection components are exposed to voltages above a predetermined threshold, the protection components conduct the default current to the ground while limiting the overvoltage to a value compatible with the capacity of the installation and equipment connected to the protection components. Such components and devices are generally designated by the term “surge protectors” or “lightning arrestors”.
In the event of a failure, in particular, at the end of their lifetime, protection components may be subject to significant heating that can cause serious damage to the installation and present risks to the user, for example, by starting a fire.
This is why overvoltage protection devices are generally provided with thermal disconnection means. These thermal disconnection means are intended to isolate the protection component from the electrical installation to be protected in the case of excessive heating of the protection component. The separation of the defective protection component from the installation to which the protection component was connected results in a suppression of the electrical power supply causing the heating and prevents the appearance or limits the harmful consequences of an excessive increase in temperature.
Generally, the thermal disconnection means include an element sensitive to the heat released by the protection component, such as a fusible solder, which, in normal operation, holds a conductor disconnection element, such as a metal spring leaf, in contact with one of the terminals of the protection component. The disconnection element is prestressed toward an open position in which the disconnection element is separated from the terminal so that, when the heat-sensitive element releases the disconnection element under the effect of significant heating of the protection component, the disconnection element moves and opens the circuit.
When the thermal disconnection means are activated, the thermal disconnection means isolate the protection component from the electrical installation to be protected, so that the protection component is incapable of conducting default currents and no longer performs the function of protecting the electrical installation.
This is why it is necessary to warn the user of any activation of the thermal disconnection means, so that the user can replace the defective device in order to continue protecting the installation.
To this end, it is known to integrate, in overvoltage protection devices, signaling means that indicate the state of the disconnection means associated with the protection components.
In particular, it is known to use visual signaling means that display, when the thermal disconnection means are activated, a warning light, such as a red-coloured surface, opposite a window located on the visible surface of a casing in which the protection component is mounted. Thus, when the user examines the electrical panel including the protection devices, the user will immediately know the state of the devices and can perform replacement operations, if necessary.
In particular, it is known to join the disconnection means using a flexible spring leaf, a signaling slider translatably mounted with respect to one of the surfaces of the casing containing the protection component, the slider being located at least partially on the path of the free end of the spring leaf when the spring leaf bends. Thus, when the protection component is disconnected, the free end of the spring leaf can interfere with the slider to exert a stress on the slider and propel the slider in translation along a trajectory substantially tangential to the spring leaf.
While these devices are generally satisfactory, the devices of the prior art can have notable disadvantages.
Indeed, the implementation of such sliders requires the production of parts with a complex shape, small size and with strict tolerances, in particular, to guide the elements in movement. Such parts are, by nature, difficult to produce and to assemble, which tends to increase the costs of production of devices equipped with them.
In addition, the devices of the prior art sometimes have reliability problems with regard to the disconnection, due to the resistance on the signaling slider opposing the opening of the disconnection means. Indeed, the slider is subjected to frictional forces that resist the movement of the slider, and the slider can even be jammed by seizing or sticking at the level of the casing, which has the effect of impeding, slowing or even prematurely blocking the movement of the disconnection leaf. Thus, in the case of a severe failure of the signaling means, the signaling means are capable of preventing the effective disconnection of a defective component, consequently, leading to dangerous heating or even short-circuiting of the installation.
In addition, the kinematic connection between the disconnection leaf and the signaling slider of the devices of the prior art is often achieved by a linear joint where an edge or a small surface element of the disconnection leaf comes into contact with a small surface element of the slider. The small area of the connection puts the connection at risk for an unexpected dislocation, in particular, when the device is subjected to vibrations or shocks, and such a dislocation would lead to a rupture in the connection and random or erroneous signaling that does not reflect the real state of the device. In addition, the fineness of such a connection makes the connection particularly sensitive to dimensional variations in the production of the constituent elements, making it necessary to maintain restrictive provisions during production and/or assembly.